The invention relates to a component placement machine with a frame and with a transport device for transporting printed circuit boards in an X-direction, which transport device comprises a transport beam extending in the X-direction, which beam can be driven in the X-direction in a reciprocating movement.
A component placement machine of the kind to which the present invention relates is known from U.S. Pat. No. 5,680,699. The transport beam in this known machine is provided with transport pins and positioning pins for the printed circuit boards. Said pins enter matching openings of the printed circuit boards. The transport beam transports the printed circuit boards in an indexing mode in the positive X-direction, i.e. the transport beam with the printed circuit boards perform an intermittent movement over a predetermined distance each time, which distance corresponds to a certain position of the printed circuit boards with respect to a component placement head. Such a movement is necessary for bringing the printed circuit boards into a desired position under the placement head so that the components can be placed in the correct positions by means of the placement head. After a number of intermittent step movements, the transport beam is at the end of its stroke and is to be returned to its starting position again. At that moment the pins are withdrawn from the holes in the printed circuit boards in that the entire transport beam is moved down, i.e. in a Z-direction perpendicular to the X-direction, whereupon the transport beam is returned to its starting position in the negative X-direction. A fresh printed circuit board may then be placed on the transport beam, and the last printed circuit board may be removed from the row on the transport beam. In view of the high accuracy with which components are to be placed and of the fact that the size of the components and the interspacings between the components on the printed circuit boards become increasingly smaller, it is necessary for said transport movements to be carried out with very high accuracy. A disadvantage of this known manner of transport is that the tool set for the positioning and transport pins present on the machine must be replaced with a different tool set whenever a different type of printed circuit board is to be provided with components. In addition, a new calibration must be carried out. All this takes much time.
It is an object of the invention to avoid the disadvantage mentioned above.
To achieve this object, the component placement machine according to the invention is characterized in that the transport device is provided with first clamping means fixedly connected to the transport beam in the X-direction for clamping in at least one lateral edge extending in the X-direction of the printed circuit boards to be transported, and in that the device is further provided with second clamping means connected to the frame for clamping at least one lateral edge extending in the X-direction of the printed circuit boards, which first and second clamping means can be brought into their active clamping positions alternately such that the first clamping means are active during the movement of the transport beam in the positive X-direction and the second clamping means are active during returning of the transport beam in the negative X-direction.
In the placement machine according to the invention, the printed circuit boards present on the transport beam are fixed by the first clamping means during the movement of the transport beam in the positive X-direction, said clamping means being active in this phase of the movement. After a number of indexing steps have been performed by the transport beam, and the latter has reached the end of its stroke, the printed circuit boards are clamped in by the second clamping means, which are activated at that moment, whereas the first clamping means are brought into their idle position. In this situation, the printed circuit boards are now fixed relative to the frame, and the transport beam can return to its starting position without taking along the printed circuit boards. The positions of the printed circuit boards in each phase of the transport through the placement machine are accurately defined in this manner without the use of transport or positioning pins. Converting of the machine to other types of printed circuit boards may now take place in a simple and quick manner, while a fresh calibration is not necessary.
One or several printed circuit boards may be present on the transport beam along the length of the placement machine. Said printed circuit boards may lie substantially against one another and may have a thickness tolerance difference with respect to one another. To guarantee that all printed circuit boards will be clamped in with a satisfactory clamping force by the clamping means, a further embodiment of the placement machine is characterized in that the first and second clamping means are formed by a number of separate clamping devices which extend in longitudinal direction one behind the other. The use of clamping devices with dimensions smaller than the dimension of each of the printed circuit boards will achieve that each of the printed circuit boards will always be clamped in by at least two clamping devices.
The placement machine according to the invention may be constructed such that the first and second clamping means extend on either side of the transport beam. This means that the printed circuit boards are gripped on both sides in a component-free zone of approximately 3 mm during operation. In an alternative embodiment of the machine according to the invention, the first clamping means are present at one side of the transport beam, and the second clamping means are present at the other side of the transport beam. This means that a component-free zone of approximately 3 mm is necessary again, but on both sides of the printed circuit boards this time, the first clamping means gripping the printed circuit board in the one zone during transport in the positive X-direction, and the second clamping means gripping the printed circuit board in the other component-free zone during the return movement of the transport beam to its starting position.
In a further embodiment of the machine according to the invention, it is equally possible that the first and the second clamping means are provided at one side of the transport beam, while the machine is provided with a guide for the other lateral edge of the printed circuit board at the other side. In this embodiment, the printed circuit board is gripped by the first clamping means during transport in the positive X-direction, while in the next phase, during the return movement of the transport beam, the printed circuit board is gripped in this component-free zone by the second clamping means.
To have a possibility of compensating for non-parallelism in the machine and sagging differences between printed circuit boards in a further embodiment of the placement machine, the first clamping means are constructed such that they clamp in the printed circuit board with a greater clamping force at the one side of the transport beam and clamp in the printed circuit board with a smaller clamping force at the other side, such that the printed circuit boards in the latter location have a displacement possibility transverse to the X-direction. The position of the printed circuit board is thus defined by the clamping means which clamp in the printed circuit boards at the one side with a great clamping force, whereas the printed circuit board has the possibility of slightly shifting in or together with the clamping means at the other side, so that non-parallelism or sagging of the printed circuit board will not lead to fractures or jamming of the printed circuit boards in the machine.
A further embodiment of the placement machine according to the invention is characterized in that the first clamping means have a jaw which is adjustable in a vertical direction transverse to the X-direction with respect to the transport beam so as to press against the upper side of the printed circuit board.